煤矿液压支架用高强钢的焊接性能

Welding properties of high strength steel for coal mine hydraulic support

为了实现Q550D高强度中厚板的高质量焊接,从而促进其在煤矿液压支架领域的推广应用,采用CO_(2)半自动气体保护焊对煤矿液压支架用550MPa级高强度中厚板进行了焊接试验,采用金相显微镜观察了焊接接头的显微组织,采用电子背散射技术和透射电子显微镜观察了焊接接头粗晶区的晶体学特征和精细形貌,采用拉伸和冲击试验机测定了焊接接头的综合力学性能。结果表明,焊接接头的屈服强度为655MPa、抗拉强度为747MPa、断后伸长率为18.5%,在母材处发生断裂;焊缝、熔合线、熔合线向外1mm、熔合线向外3mm和熔合线向外5mm处的-20℃冲击吸收功分别为82、113、106、124和159J;焊缝、粗晶区、细晶区、临界区和母材各区域的平均硬度值分别为294.07HV、293.18HV、264.67HV、275.02HV和278.49HV。与母材相比,焊缝和粗晶区为局部硬化区,硬化率分别为5.59%和5.27%,细晶区和临界区分别为局部软化区,软化率分别为4.96%和1.25%。高位错密度的针状铁素体板条纵横交错、彼此咬合,可有效阻碍裂纹的扩展,从而改善了粗晶区的力学性能;粗晶区原奥氏体晶粒内部生成的粒状贝氏体、条状贝氏体和针状铁素体的大角晶界比例为72.12%、平均等效亚晶粒尺寸为1.28μm,高比例大角晶界和小尺寸等效亚晶粒可有效抵抗解理裂纹扩展,是试验钢焊接接头低温冲击韧性优异的主要原因。

In order to realize the high quality welding of Q550Dhigh-strength mid-thick plate,and promote its popularization and application in the field of coal mine hydraulic support.The welding test of 550MPa high-strength midthick plate for coal mine hydraulic support was carried out by CO_(2)semi-automatic gas-shielded arc welding.The microstructure of welded joint was observed by optical microscope.The crystallographic characteristics and fine morphology of coarse-grained heat-affected zone in welded joint were observed by electron backscattered diffraction and transmission electron microscope.The comprehensive mechanical properties of the welded joint were measured by tensile and impact testing machines.The results showed that the yield strength and tensile strength of the welded joint are 655MPa and 747MPa,respectively.The elongation is 18.5%,and the fracture occurs at base metal.The impact energy of weld metal,fusion line,fusion line outward 1mm,fusion line outward 3mm and fusion line outward 5mm at-20℃are 82,113,106,124and 159J,respectively.The average hardness of weld metal,coarse-grained heat-affected zone,fine-grained heat-affected zone,intercritical heat-affected zone and base metal are 294.07HV,293.18HV,264.67HV,275.02HV and 278.49HV,respectively.Compared with the base metal,the weld metal and coarse-grained heat-affected zone are local hardening zone with hardening rates of 5.59%and 5.27%,respectively.And the fine-grained heat-affected zone and intercritical heat-affected zone are local softening zone with softening rates of 4.96%and 1.25%,respectively.The acicular ferrites with high dislocation density crisscross and bite each other,which can effectively prevent crack propagation and improve the mechanical properties of the coarse-grained heat-affected zone.The large angle boundary ratio of granular bainite,strip bainite and acicular ferrite generated within the parent austenite grain in the coarse-grained heat-affected zone is 72.12%,and the average equivalent subgrain size is 1.28μm.High proportion of large-angle grain boundaries and equivalent sub-grains with small size can effectively resist crack propagation,which is the main reason for the excellent low-temperature impact toughness of the welded joint.